What causes seasonality of birth in schizophrenia?

Evidence of a latitudinal gradient in the age at onset of schizophrenia

Variation in the age at onset of a multifactorial disease often reflects variation in cause. Here we show a linear latitudinal gradient in the mean age at onset of schizophrenia in 13 northern hemisphere cities, ranging from 25 years old in Cali, Columbia (at 4 degrees north) to 35 years old in Moscow, Russia (at 56 degrees north). To our knowledge, this striking association has not been previously reported. We consider several explanations, including the effects of pathogen stress, natural selection, sexual selection, migration, life-history profiles, or some combination of these factors, and we propose a test of competing causal hypotheses.

Variation in incidence of neurodevelopmental disorders with season of birth

BACKGROUND

The etiologies of autism spectrum disorder and many neurodevelopmental disorders are largely unknown. The detection of a seasonal variation of birth of children diagnosed with a certain disorder could suggest etiological factors that follow a seasonal pattern. We examined the seasonal variation of births of children diagnosed with any of 4 common childhood neuropsychiatric disorders: autism spectrum disorder, hyperkinetic disorder, Tourette syndrome, and obsessive-compulsive disorder.

METHODS

The study cohort consisted of all children born in Denmark from 1990 through 1999 identified in the Danish Medical Birth Register (n = 669,995). Outcome data consisted of both inpatient and outpatient diagnoses reported to the Danish National Psychiatric Registry from 1995 through 2004 using the International Classification of Diseases, 10th edition, diagnostic coding system. Logistic regression combined with spline (a smoothing method) was used to estimate the variation with season of birth for each disorder. Estimates of risk of each disorder with season of birth were adjusted for differences in follow-up time and change in incidence over time.

RESULTS

No convincing variations in season of birth were observed for any of the 4 disorders, or for the autism-spectrum-disorder subtypes.

CONCLUSION

Although we cannot rule out the possibility of seasonal variation of birth for a range of childhood neurodevelopmental disorders, we find little evidence that seasonal environmental factors are related to these disorders.

Chronic administration of clozapine alleviates reversal-learning impairment in isolation-reared rats

Isolation rearing has been used for inducing schizophrenia-like symptoms in rats. Human schizophrenics have deficits in prefrontal-dysfunction-related cognitive/behavioral flexibility. Rats with lesions of the medial prefrontal cortex perform poorly in reversal learning. It is uncertain whether isolation rearing, however, causes reversal-learning impairment in adult rats. Using the rotating T maze, this study examined the effect of chronic administration of clozapine on visual discrimination learning and reversal learning in isolation-reared and socially reared adult rats. The results show that isolation-reared rats without clozapine injection performed significantly worse than socially reared rats in reversal learning but not in acquisition learning. Chronic injection of clozapine (5 or 10 mg/kg) in isolation-reared rats significantly improved reversal learning but had no effects on acquisition learning. Further data analyses show that in both the inhibition phase and the new-strategy-acquisition phase of reversal learning, isolation-reared rats needed significantly more correct-response trials to reach the criterion than socially reared rats, and clozapine significantly reduced the isolation-induced impairment of reversal learning only in the new-strategy-acquisition phase. In socially reared rats, clozapine had a dose-related interfering effect on reversal learning but not acquisition learning. This study supports the use of isolation rearing as a model for investigating the neurodevelopmental hypothesis of schizophrenia.

Applications and limitations of empiric data in provision of recurrence risks for schizophrenia: a practical review for healthcare professionals providing clinical psychiatric genetics consultations

Schizophrenia is a common disorder that may frequently be encountered when taking family histories in the genetics clinic, whether or not the referral is for a psychiatric indication. Like in other common disorders, the provision of recurrence risks for schizophrenia is a complex clinical issue because empiric recurrence risks (while reasonably well established) can rarely be used without individual tailoring. This review seeks to identify and detail some pertinent issues surrounding the clinical utility of empiric recurrence risks for schizophrenia, and to provide an overview of important factors to consider when tailoring empiric risks for individual patients.

Season of birth, age and negative symptoms in a Xhosa schizophrenia sample from the Southern Hemisphere

OBJECTIVES

Seasonality of birth, more specifically winter/spring births, has been implicated as a risk factor for the development of schizophrenia. The primary aim of this study was to determine whether schizophrenia patients of Xhosa ethnicity born in autumn/winter have different symptom profiles to those born in spring/summer. The secondary aim was to determine whether the autumn/winter and spring/summer birth rates for schizophrenia patients of Xhosa ethnicity were similar to that of the general Xhosa population.

METHOD

Individuals with a diagnosis of schizophrenia, born in the Western and Eastern Cape Provinces of South Africa (n = 386), were categorized as autumn/winter-born (March to August) patients or summer/spring-born (September to February) patients. Negative global scores of the schedules for the assessment of negative symptoms were categorized as normal (rating of 0 and 1) or positive (rating of 2 to 5).

RESULTS

Patients born in autumn/winter were more likely to have avolition/apathy than those born in summer/spring. The results also showed that the age of the patients played a significant role in modifying the effect of the season of birth on symptoms of schizophrenia. Especially older people (more than 30 years old) born in autumn/winter had a higher incidence of avolition/apathy than those born in summer/spring (p = 0.026). Furthermore, in the relationship of birth season and avolition/apathy, the marital status of the patient was a significant independent explanatory variable, while gender was not. The study also showed a spring excess of 4% in birth rate compared with the general Xhosa population.

CONCLUSION

The results from our study support the existence of a seasonal birth pattern in an African schizophrenia population and suggest that avolition/apathy may underpin this seasonal pattern.

Prevalence of Toxoplasma infection in first-episode schizophrenia and comparison between Toxoplasma-seropositive and Toxoplasma-seronegative schizophrenia

OBJECTIVE

To compare the prevalence of Toxoplasma infection between the first-episode schizophrenia and the controls and to compare the clinical features between the Toxoplasma-seronegative and Toxoplasma-seropositive patients with schizophrenia.

METHOD

The rate of serum reactivity to Toxoplasma in 600 schizophrenia, 600 affective disorders, and 400 controls was investigated. The clinical symptoms of the schizophrenia patients were scored and compared.

RESULTS

The rate of IgG antibody, not IgM in the schizophrenia patients, was higher than the control groups, and the odds ratio of schizophrenia associated with IgG antibody was 2.22-5.12. The affective disorders did not differ in the rate of IgG or IgM antibody from the normal or the physical disease control. The seropositive schizophrenia patients had higher scores on the positive subscale and three components of Positive and Negative Symptoms Scale than the seronegative patients.

CONCLUSION

This study lent further weight to the hypothesis that exposure to Toxoplasma may be a risk factor for schizophrenia.

Melatonin receptor (MT1) knockout mice display depression-like behaviors and deficits in sensorimotor gating

Although critical for transducing seasonal information, melatonin has also been implicated in several physiological systems, as well as the regulation of behavioral and cognitive processes. Therefore, we investigated the neurobehavioral effects of mice missing the type 1 melatonin receptor (MT1). Male and female MT1 knockout (MT1-/-) and wild-type (WT) mice were tested in the acoustic startle/prepulse inhibition (PPI), open field and Porsolt forced swim tests. Male and female MT1-/- mice displayed dramatically impaired prepulse inhibition in the acoustic startle response. Female WT mice were more active in the open field than WT males. However, male and female MT1-/- mice did not differ in total locomotor activity. WT animals spent significantly more time in the center of the arena (a behavioral outcome associated with reduced anxiety-like behavior) than MT1-/- mice. Also, the sex difference between male and female WT mice in the amount of time spent in the center versus periphery was not observed among MT1-/- mice. Both male and female MT1-/- mice significantly increased the time spent immobile in the forced swim test, an indication of depressed-like behavior. The lifetime lack of MT1 signaling contributes to behavioral abnormalities including impairments in sensorimotor gating and increases in depressive-like behaviors. Taken together, MT1 receptor signaling may be important for normal brain and behavioral function.

Schizophrenia: An Update and Review

Schizophrenia is a common complex disorder characterized by psychosis, cognitive dysfunction and negative symptoms, whose etiology involves interactions between both genetic and environmental vulnerability factors. Recently, ongoing research attempting to elucidate the nature of these vulnerability factors has been generating exciting findings. The advances in understanding of environmental risk factors for mental illnesses and in genetic research into mental illnesses will be reviewed. Limitations of the findings and implications of these advances for genetic counseling practice will also be discussed.

Do maternal folate and homocysteine levels play a role in neurodevelopmental processes that increase risk for schizophrenia?

OBJECTIVE

Evidence from many different lines of research supports the hypothesis that schizophrenia is a disorder of development with etiological factors implicated as early as the second trimester in utero. We suggest that low maternal folate, acting to increase homocysteine levels, may provide a functional link between many of the identified prenatal risk factors and the hypothesized mechanisms whereby neurodevelopmental patterning deviates toward a schizophrenic potential.

METHODS

PubMed was searched from the present back to 1963, when elevated homocysteine was identified as a pathogen in homocystinuria as first described by Carson and colleagues (Arch Dis Child 1963;38:425-36). All articles for homocystinuria, homocysteine, folate, and development with schizophrenia were evaluated.

RESULTS

The findings from this review support the hypothesis that maternal low folate and high homocysteine levels may provide a potential teratogenic mechanism that increases the risk for developing schizophrenia.

CONCLUSION

The potential role of maternal folate deficiency and hyperhomocystinemia in the genesis of schizophrenia would extend the range of their known teratogenic effects. Given the potential for preventive treatment offered by this hypothesis, we believe further investigation into this mechanism is warranted.

Seasonal variations of cerebral palsy births in northeastern Poland

BACKGROUND

The objective of this report was to examine the seasonal variations on the incidence of cerebral palsy (CP) in Podlasie province, Poland in a retrospective case-control study.

METHODS

Data were obtained from the Department of Pediatric Neurology and Rehabilitation. Selected babies were all born between January 1, 1990 and December 31, 1999; 212 children (116 boys, 96 girls) with CP were included in the study. We applied Cosinor analysis to examine the seasonality of CP births.

RESULTS

The highest number of CP births occurred in spring and the lowest in winter, with intermediate values in summer and autumn. This seasonal pattern was significant for spring vs. winter. The peaks in CP births occurred in May and August. The lowest number of CP births occurred in February and December. We also demonstrated seasonal variation in CP births in girls and boys and Apgar score. Peaks in CP births in boys were noted in May and October and Apgar score in May and December, respectively. No significant relationship between mean temperature and Apgar score, low birthweight and asphyxia was found.

CONCLUSIONS

These data suggest the seasonal patterns of CP births. Further studies should be performed with larger numbers of patients.

Seasonality of schizophrenia births in the Japanese population: increased winter births possibly confined to the north area

A number of North American and European studies have observed a higher proportion of winter births in schizophrenia patients. Thus, seasonal fluctuation of unknown environmental factors may affect brain development in ways that alter susceptibility to schizophrenia. Specification of these factors may help elucidate the etiopathological mechanism of the disease, about which little is certain. A small number of studies have investigated this issue in Asian populations, and the findings are not as consistent as those of Western populations. No remarkable excess of winter births has been observed in Japanese or Korean studies, while some studies have reported a significant decrease of summer births. We further investigated the issue in Japanese patients with schizophrenia (n=3927). No significant excess of winter births was observed, but a decrease in the summer births was found in male subjects. This is largely consistent with previous Japanese studies; however, when the subjects were confined to those born in a colder and higher latitude area of Japan (n=1338), a consistent trend for both a winter increase, and a summer decrease, was found. However, the results did not consistently reach statistical significance, possibly due to the lack of statistical power. Environmental factors that correlate with latitude might play a role in the development of the seasonality of births in schizophrenia. Further studies in a larger sample size are required to test these possibilities.

Season of birth effect on personality in a general population

Seasonality of births in schizophrenia and other mental disorders has been consistently observed. This may be through effects of unknown environmental factors that seasonally fluctuate on the brain development. The effects may affect cognitive function of the brain and behavioral characteristics that might be correlated with the development of personality not only in patients with mental disorders but also in healthy subjects. We, therefore, investigated the effects of season of birth on personality traits in healthy Japanese adults (n = 397). Personality traits were evaluated using the NEO Personality Inventory-Revised (NEO PI-R). A trend for lower Agreeableness in subjects born during winter (December to February) than other subjects was observed (P = 0.036, after correction for the multiple testing, multiple regression analysis adjusting for age and sex). Other major factors of the NEO PI-R, including Neuroticism, Extraversion, Openness and Conscientiousness, were not affected by season of birth. Further studies may be recommended to confirm the results, considering the relatively limited sample size. Evaluation of cognitive functions and behaviors using other measures including event-related potentials and functional MRI may also help the interpretation of the present result.